Do aquatic plants prefer ammonium

OK, here is the article http://depot.knaw.nl/3383/1/21273.pdf cited by Diana Walstad to show that aquatic plants prefer ammonium. After reading the original research, I was confused with the results, especially figure 4 and 5.

First of all, the dry weight increase of E. nutallii did not correlate closely with the nitrogen absorbed, either NH4 or NO3. I am not sure if luxury uptake by the plants could explain that, or maybe there were some other confounding factors.

BTW, all treatments including the controlled experiment, the NH4 level did not go to 0 after 14 days. In treatment 2 with 2 mg NO3 added, NH4 actually increased in 14 days. Unfortunately the author did not show detailed data about the nitrogen levels. This is interesting to me, but I have no idea how to explain that.

Staff MemberAdministrator

I'm not comfortable with the citation. Unless you can show an increase in the tissues levels for N before, after treatment, you really cannot say if it was uptake, that is the 2nd conformation step that should be done if you do any uptake studies with aquatic plants. I could not do this study without having done that step where I work.
That would be another test I'd have to do.

I could also radio label the N from each source and see also using 15NO3 and 15NH4 in separate test, then measure the amounts and rates of uptake.

There's is a trade off in the study, they only did short time exposures, it's hard to do long term studies on uptake and we do not see the same pattern with dry mass increases with responses to uptake. The prediction falls short based on uptake over short time frames.
Luxury uptake is only considered over short time frames also, not over seasonal time frames and pulse flows that typically occur in natural systems.

Say they have a large pulse flow in the spring runoff of PO4, then taking up 10X more than you need to normal growth is required, because the rest of the year, the PO4 will be absent. Or they save the PO4 for production of seeds, flowers, tubers etc even though at the time, back in say May, they did not need it then.
Plants rarely waste energy and resources.

I agree that generally we see plants using some NH4 if it's available.
But how it's available is a key for us, soil seems a good long term non toxic source, fish in the water column seems another.

My question is much more about who gets that NH4, bacteria? Or plants?
A well run planted tank also has a strong stable Bacterial community, just like a fish only aquarium that's been dosed with NH4 using fishless cycling or slowly added fish loads.

If you start dosing small amounts of NH4, this does the same thing. Are you just enhancing the filter's bacteria slowly to handle and oxidize more NH4 ?
Or, are the plants really taking this NH4 up? The paper did not add this critical factor.
Does this NH4 really enhance aquatic plant growth rates?
In the paper, that was no different.

In our own aquariums, we see little differences when NH4 is dosed to the water column, which was specific to that study.

Sediment dosing of NH4? I think there's more to that and we can see some differences, but the water column? I'm not so sure we can say a whole lot comparatively. After a few days, bacteria form and start skewing this process.
I think you have a few things going on with this paper which makes for a good student discussion of the problems and how we might test further to get around these short falls in our questioning.
I would not use it as a sole source of support, and it is dose response related and a lot more lethal than NO3.

thanks for the reply. In another thread you explained to us with this article http://wetlands.ifas.ufl.edu/publications/PDF-articles/96.pdf, which showed that rapid disappearance of NH4 was probably the result of active nitrification, but not the uptakes by the plants. That's why I intended to read the original study from Ozimek, I tried to find out whether bacteria or plants consumed NH4, obviously I did not find the answer, but only more questions.

Staff MemberAdministrator

thanks for the reply. In another thread you explained to us with this article http://wetlands.ifas.ufl.edu/publications/PDF-articles/96.pdf, which showed that rapid disappearance of NH4 was probably the result of active nitrification, but not the uptakes by the plants. That's why I intended to read the original study from Ozimek, I tried to find out whether bacteria or plants consumed NH4, obviously I did not find the answer, but only more questions.

"We assume, for our purposes here,
that the macrophytes collected for isotopic analysis
(mainly Myriophyllum spicatum L., Potamogeton pectinatus
L. and Vallisneria americana Michx.) acquire, in
large part, nitrate from the water column. There are,
in fact, numerous studies indicating that nutrient
uptake by these taxa can occur through the leaves (e.g.
Best & Mantai, 1978; Van Wijk, 1989; Madsen &
Cedergreen, 2002). Moreover, the potential for nutrient
uptake through the leaves is likely to be
relatively greater in the water column compared with
the sediment. Although water flow is often reduced in
macrophyte beds resulting in the formation of
boundary layers (Madsen & Cedergreen, 2002),
nutrient supply in the sediments is restricted as a
consequence of both diffusion and by binding of
nutrients to the sediment matrix. In addition,
N-nutrients taken up by roots are mainly incorporated
in root tissue while nutrients taken up by leaves are
mainly incorporated into the above-ground plant
biomass (Nichols & Keeney, 1976)."

I'd suggest using sediment NH4/NO3 in the water column, something I've done for a long time.
Either way, no matter what is foiund/shown, debated which is better, you have covered both locations and types of N.

We are less concerned about the theory as horticulturalist and more about management.
For just the best management practice(BMP), I think we have long solved this issue for aquariums.

Some can stay stuck in the mud, and debate the points, scream liud that one is preferred over the other, either or dicotomies..........without looking at the more larger relevant issue for aquarist.
We have many species with many differing preferences, so to meet all the needed, add to sediment and the water column.
Since NH4 can bind well to clays and is toxic at high levels in the water, we add that to clays sediments.
Since NO3 does not bind well, and is non toxic relatively, we add that to the water column.

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